The production of veneer for a variety of different purposes including plywood manufacture, laminated veneer lumber or, in some cases, oriented strand lumber, it is common practice to mount wooden bolts on a lathe and rotate same around an axis substantially parallel to the longitudinal axis of the tree from which the bolt was formed, i.e. with the annual rings extending circumferentially about the axis of rotation. In such systems as is well known the cutting edge of the knife is mounted substantially parallel to the axis of rotation and is held in this parallel orientation as it is advanced toward the axis as the log is peeled thereby to produce a substantially uniform thickness veneer (there will be some deviation due to defects, etc) and a substantially right cylindrical core when the peeling operation is completed. It will be apparent that as peeling occurs since the knife edge remains parallel to the axis of rotation, the veneer produced is of uniform thickness and the length of each side edge of the veneer is the same so there is little tendency for the veneer to curl.
It is also been suggested to cut tapered veneers particularly for the production of the walls of a bucket by mounting the blade on an arm and pivoting the arm around a center pin located axially spaced from the end of the bolt. Such devices are shown in U.S. Pat. No. 767,466 issued Aug. 16, 1904 to Wolfinger and U.S. Pat. No. 1,209,052 issued Dec. 19, 1916 to Sinclair. These devices cut on a taper so that the veneer produced is necessarily thicker at one end than other and with one side edge longer than the other so the veneer will tend to curl.
U.S. Pat. No. 1,957,166 issued May 1, 1934 to Hartzell also discloses a concept of cutting a veneer basically in the same manner as some pencil sharpeners operate.
It is common practice to sense the bolt as it approaches the lathe to provide an indication of the taper and shape of the bolt and then to grip the bolt in a particular fashion so that it may be mounted in the lathe in a selected position to determine the location of the axis of rotation of the bolt in the lathe and thereby to maximize the amount of veneer produced from a given bolt.
In modern lathes, the peeling knive is mounted on a knife carriage which in turn is mounted on a pair of side blocks one at each end of the carriage. The side blocks are mounted in tracks and are advanced by a suitable feed mechanism one at each side of the machine controlled to advance the carriage with the knife substantially parallel to the axis of rotation of the bolt, i.e. with both axial ends of the knife travelling at the same speed. In many of the modern machines, the rate of advance or degree of advancement of each side block is continuously measured to ensure that the knife carriage presents the knife edge substantially parallel to the axis of rotation throughout the peeling operation. In many cases, such a system includes independent hydraulic drives for each side block, measuring the displacement of each side block and controlling the operation of the hydraulics to ensure that the side blocks are properly aligned to maintain the knife edge as above described.
It has been known on startup to cut veneer with the blade misaligned so that the cutting radius at one end of the block is shorter than at the other thereby producing a veneer longer on one side than the other forcing the same to curve. Such a condition while known to happen could not be tolerated for any significant length of time and thus was corrected immediately.